Capacitor sealing method



Aug- 13, 1963 L. L. RICE ETAL CAPACITOR SEALING METHOD Original Filed Jan. 12, 1959 2 u l w 7 A w i w INVENTORS LIVINGSTON L. RICE I WALTER J. ROHANE BY w W F IG.4

T H E I R ATTORNEYS ,UnitedStates 3,100,330 CAPACITOR SEALING METHOD Livingston L. Rice, Williamstown, and Walter J. Rohaue, Adams, Mass, assignors t Sprague Electric Company, North Adams, Mass., a corporation of Massachusetts Original application Jan. 12, .1959, Ser. No. 786,277.-

" Divided and this application Nov. 21, 1960, Ser. No.

2 Claims. (Cl. 29-155.55)

This invention relates to capacitor terminal constructions and a process for producing the same and, more particularly, to a method .for sealing the .end of a capacitor at the terminal lead. This application is a division of our copending application SN 786,277 filed January 12, 1959.

Electrical components such as electricalcapacitors com-' prise capacitance sections having terminal lead-wires extending therefrom. The sections are enclosed in casings with the terminal leads extending through the ends of the casings. The extending terminal leads provide means for electrical attachment to the contained section. In one typeof capacitor a cylindrical capacitor section is mounted in a tubular casing. One of the more commercially acceptable capacitor constructions is the socalled extended-toil capacitor which comprises at capacitor section of electrode and dielectric ribbons convolutely. wound with one of the electrode ribbons extending beyond the dielectric'ribbons at one end of the convolnte roll and another of the electrode ribons extending beyond the dielectric ribbons at the other end of the roll. Fheroll is customarily a compact tightly Wound snbasssembly in which the extended foils at each ,end are convertcd'intoa .single terminal, as by [the application of solder., To the common terminal formed by the solder operation there is applied a lead-wire which makes good electrical and mechanical contact with the extended foil. The lead-wire has an elongated mem- 'ber extending substantially axially from the convolutely wound roll. This subassembly carrying the attached lead- "fthe tubular casing. Each plug is provided with a passage. means through which the respective lead-wire extends. Both ends of the rolled section are insulated from contact with the casing which may .be composed of metal.

The; end-seal member provides the insulation of the casing item the su-bassembly. The end-seal itself must be sealed so as to provide a complete closure otthe capacitor section within the casing. This involves the sealing of the end-seal around the lead-wire. In the assembly of the parts, the end-seal must be provided a. sutficient passageway so that the lead-Wire can be inserted through the end-seal. Also, in some construc- Itions, it is necessary to provide a sufficient passageway 3,100,330 Patented Aug. 13, 19.63

expensive material which is resistant to chemical action by the Various dielectric impregnants.

The casing containing the capacitor section is sealed at an elevated temperature to create a partial vacuum within the casing, so as to militate against later explosion from the expansion that takes place when a unit becomes heated during use. As a result, creating the seal around the external extending lead-wire should act to bothcooperate with the creation of this partial vacuum I within the casing and also result in a hermetic seal which preserves the partial vacuum. Particularly to be avoided is the sucking into the casing of melted sol der that may occur whenthe partial vacuum is broken.

It is an object of this inevntion to provide a method of sealing a capacitor terminal closure that effectively seals an encased capacitor section.

Another object of this invention is to provide a method \for sealing betweenan extending component lead-wire and a casing closure member such'that the seal is not opened by the application of heat to the seal parts, so as to retain either vacuum or pressure Within the casing.

It is a still further object of this invention to provide a method for producing an end-seal at an externally extending lead-wire of an electrical component, which seal does not impair the electrical characteristics of the lead wire or its physical strength.

I Still another object of this invention is a semiautomatic procedure for producing a crimped joint which is hermetically tight.

These and other objectsof this invention will become apparent from the following description taken in conto'permit theintroduction of impregnant into the interior junction with the accompanying drawing, in which: I FIG. 1 isan axial section partly in elevation of an .electrical capacitor containing the invention;

. This invention seals the end of a capacitor casing'with' a metal-to-metal hermetically tight contact between a lead-wire and a lead enveloping tubulation. The tubulation in turn is mounted in a plug assembly which is sealed to the casing, as by jammingthe casing rim into the. plug periphery. I a

Referring to H6. 1, a capacitorlO- is shown having a cylindrical casing 11 with its respective open ends each closed with an end plug 12. The end plugs 12 are sub stantially identical both in their constitution and in their relationship to the casing '11. Each end plug 12 of this invention is made up of a metal compression ring 13 and a glass annulus 14. Each glass annulus 14 is contained within and sealed to the respective donut shaped comp-ression ring 13. Each glass annulus 14 has a tubulation 16 sealed inits central passage and extending axially outward from the end plug 12. 'Each tubulation 16 is shown as having a terminal lead-wire 19 extending axially therethrough. Each end plug 12 is retained in the respective open end of the casing 11 by engagement with a respective rim 18 of the casing 11. Each compression ring 13 has a peripheral groove 17 which receives the respectiverim 18 of the casing 11, which is indented into the respective groove 17 by \forming. l

capacitance section 20, contains foils 21 and 21'. 21 extends from one end of section 20 and foil 21' extends wire 19 and the tubulation 16 is slight.

The casing llcontains an active component in the form of an extended foil capacitor section 20. The section 20 The Foil is suitably prepared and inserted in the casing 11.

from the opposite end of section 20. The extended 'foils are wiped with solder to provide a solder, terminal 32 which functions as a seat for the so-called pig-tail of lead-wires 19 Each of the leads 19 is in contact with the extending turns of one of the foils at its respective end of section 20. The lead-wires 19' contact the soldered :extended turns of the foils and extend to the exterior of the capacitor through a passage 30* in the respective tubulations 16. I Each lead-wire 19 is retainedwithin the passage 30 and in position with respect to capacitor section 20 by the novel crimp structure of this invention. The tubulation 16 is mounted in the end plug 12. and has sufficient internal diameter so that a'space 29 is provided I in passage 30 between lead-wire 19 and the inside of tubulation 16 to permit lead-wire 19 to pass easily through passage 30. This arrangement contributes to easy assembly ofthe parts.

In the illustration of FIG. 2 the central portion of one lot the end plugs 12 is shown on an enlarged scale. The

glass annulus 14 is bonded to the tubulation 16 by a suitable glass-to-metal bond. This bond is hermetically tight and permanently anchors the tubulation 16 in the annulus 14; against detachment or leakage. As shown in the enlarged drawing of FIG. 2 the spacing between the lead- In FIG. 2 the radial spacing of the parts is exaggerated to better illustrate this invention. In actual practice the lead-wire 19 is just small enough to fit through the passage 30. In

" vthe figures the clearance 29 between the outer periphery of lead-wire 19 and the inner surface of tubulation 16 is exaggerated for the purpose of illustration,

The lead-wire 19 is a tinned wire of suitable characteristics for effecting electrical connection to the capacitor section 20 through the respective foils 21 and 21'. The tubulation 16 has a tin coat 23 which covers both the inner and. outer surfaces of the tubulation. The leadwire 19 is provided with a layer of tin 25 applied over a copper surface. The tin coating 23and the tin surface jlayer -25a-re shown invsection on the tubulation' 16 and r the wire .19 respectively in FIG. 2. The seal of tubu1a tion 16 onto lead-wire 19 in final form is illustrated in FIG. 3. In the area of the crimped portion 26 the base metal of the tubulation 16 is brought into face-to-faoe contact with the copper metal of the lead-wire 19. The

contact extends along the surfaces of the two axially extending parts (tubulation '16 and lead-wire 19) and forms a mechanical joint between the parts along this area of contact that is hermetically tight. Adjacent to this hermetically tight joint there are formed rings 27 of displaced tin. These rings .27 are located at the respective ends of thefcrimped portion 26 and lie within thetubula- "tion 16 in the'clearance space 29.

- The sealed relationshi between the sleeve 16and the wire 19 is brought into effect by a two-stage crimping op,-

eration. In the drawing the result of the first stage operation is illustrated in FIG. 2, and the result of the second stage operation is illustrated in FIG. 3. 7

Suitable means for crimping tubulation =16jinclude a four-jaw chuck in which the jaws are heated .to above the flow temperature of the tinned coatings on tubulation 16 and lead-wire 19. The first stage operationcollapses the tubulation 16 inwardly of its axis against the lead-wire 19.

and its surface layer 25. In' collapsing stubulation 16 against'lead wire 19, the slight clearance 29 between the inside of the tubulation 16 and the outside of the leadwire 19 is closed to bring the inner coat 23 against the surface layer 25 at the crimped portion 26.. In this stage 'of the crimped portion 26, the respective inner=and outer surfaces are brought into contact and are heated to above the flow temperature of the coatings on the surfaces.

rials fiow under pressure.

The second stage of the crimping process brings the tubulation 16 and the lead-wire 19 into tight sealing rela''- ,tionship. In FIG. 3 the crimped portion 26 is shown atthe completion of the second stage of the crimping process,

In the second stage of the crimping process, the heated.

crimping jaws vare forcibly applied against the crimped portion 26 to effectflowof tin coat 23 on the inside of tubulation 16 and layer 25 on lead-wire 19 which had been sufliciently softened and melted during the first stage.

Sufficient force is applied through the crimping rneanst'o bring the base metal of thetubulation 16 into contact with the copper of the lead-wire 19. The tin coatings flow out of the area of the crimped portion 26. The tin coat flows both on the outer surface of the lead-Wirej19 and on the inner surface of the tubulation 16. The crimp ing means are heated to about 100 C. above the flow point of the tinned surfaces so that the surface mate- 'The result is a mechanical joint in the area of the crimped portion '26 between the inner surface of tubulation :16 and the outer copper surface of lead-wire 19'. The vacuum tight seal that results is between the base metal of the respective parts, tubula The construction of crimp 26 and its location on tubu lation 16' are such that no'strain is placed on glass mem- I ber 14.

The three parts of end-seal plug .12, namely the tubulation '16, the glass annulus 11-4 and the compression ring 13, are sealed together andfunction to provide-a hermetically tight plug. The crimp portion 26 secures 7 the lead-wire .19 in this end plug 12'a-nd terms theher- I metically tight seal therewith. i

A dielectric spacer annulus 28 is positioned between the capacitorlsection 20 and therend plug 12 at each of the respective ends of the capacitor 10. The respective spacers '28 fit between the inner surface of the end plug 12 and the parts Wllhllls the casing 11 as shown at the I inner ends of the leads'19 in FIG. 1.

' The casing 11 is formed of a malleable material that can be, spun and Worked particularly at its edges. In

' FIG. 4 the junction of the end plug 12 with the rim 18' of the casing 11 is shown. The groove 17 in the circumferential peripheral surface of thering 1-3 and the rim 1-8 of the casing 11 overlap'to a point where the casing .11 can be readily formed to extend into the groove '17.

groove 17, in the form of an indentation. The rim 18 is placed between lateral walls of the groove 17. Thus,

in the assembly of the capacitor 10 a stru-ctur'alicomiection is achieved between the end plug 12 and the casing 111 by the contact of the rim' 18 in the ring -13braced between the sloping sides of the Vshaped groove '17 The fit of the parts is part of the moisture barrier of the end plug .12 in the capacitor 10. This moisture barrier prevents the penetration of moisture into the casing and f egress of material from within the casing. After the lip 18 is indented into the groove 17 the connection of the end plug 12 in the capacitor is completed by ,fill ingthe groove 17 with solder to cover the rim 18 from theoutside and assists in creating the hermetic seal of the end plug 12 at this point. Indentation ofrim 18 into. groove 17 in the manner shown in FIGS. 4 and 5 enables-thefl solder to be applied externally of casing 11, and hence; j avoids all the disadvantages of blind solderingthat are inherent in prior art methods of closing capacitor cas- I ings. With the solder applied to the rim 18 in the groove 17 the fastening of the end plug .12 in the casing 11 is completed. n

Inthe embodiment of this invention described in connection with 'FIGS. 13, section 2 0 comprises twoelec- !In FIG. 5 the 18 is shown worked intothe.

trodes convolutely Wound in extended-foil fashion with suitable layers of dielectric material between the electrodes. One electrode 21 is shown as the foil which extends at the one end of the section, and the other electrode 21 is shown as the electrode which extends at the other end of the section. Dielectric material is wound with the foils to provide the proper spacing of the toils. However, it will be understood that other type-s of capacitors and other electrical components can be contained within the sealed casing of this invention.

The casing 11 is shown sealed at both ends. The casing 11, however, may have a closed bottom at one end so as to receive the end plug .12 in only one end. Thus, while the invention has been described above as applied to a capacitor containing a dielectric impregna-nt within a metal casing, it will be understood that the above description and illustration is set forth for the purpose of presenting an embodiment and that this invention is applicable to other components. Various other modifications may bemade to the above-described embodiment without departing :from the spirit of this invention.

-While the surface coatings 23 and 25 have been described as tin layers, it should be understood that any of the well known tin-lead solder formulations which are frequently employed in capacitor constructions may be utilized in the practice of this invention.

This invention avoids the disadvantages in prior sealing arrangements resulting from prior methods of sealing. An advantage is obtained in melting and displacing the tinned coatings in such a manner that the coating material is moved only to the immediate adjacent area and are cooled and retained permanently. This is .the result of the local heating at the crimp portion with the maintenance of a relatively, cool condition in the sleeve and lead at more removed portions. It the tinned coatings were subjected to more general heating they would move alongmore extensive areas of the parts. Under such conditions the low pressure within the casing 11 could cause the melted tin flow to be sucked into the interior of the unit whenever the capacitor was subjected to reheat in its circuit applications.

The capacitor of this invention is adapted to withstand temperatures of over 150 C. in operation without effect upon its end seal. It will be seen that the temperatures outside of the casing may exceed the melting point of the I tin solder coat Without opening the crimp 26.

A further advantage of'this invention isfound in the fact that no additional means of sealing at the terminal Wire is necessary. The mechanical joint that is formed between the eyelet sleeve and the terminal wire is vacuum tight. This is not a solder seal but a true base metal-tobase metal interface of the parts. As such there is no danger of tin flow upon reheating as noted above. Another advantage of the mechanical grip 'between the tubulation and the lead-wire is the fastening of lead-wire 19 in tubulation 16 to avoid endwise movement and strain on solder contact 32 with the capacitor foil.

The crimping process is advantageous in dividing into two stages the operation of sealing the tubulation or eyelet to the terminal lead-wire. The important second stage can be concentrated and confined in nature. Stated otherwise, t-he eyelet surface is brought into contact with the lead-wire in the first and relatively non-critical stage of operation. Then the two parts can be sea-led by a positive action which is more limited in duration as a result of the first stage preparation. Further, although the lead wire is tightly contained within the eyelet that surrounds it, it is not worked or thinned by the crimping action in the sealing operation and the copper surface of the wire remains unaffected with very little diameter change.

, When the unit is soldered in a circuit the heat for soldering applied to the terminal lead-wire cannot cause the seal of the lead to be destroyed.

What is claimed is:

a 1. The method of sealing an electrical component casing, said method comprising compressing a portion of a close-fitting tinned tubulation of an end seal onto a tinned lead-wire extending from an encased electrical component through the tubulation, heating said tubulation and said lead-wire at the compressed portion to melt the tinned coats, displacing said tinned coats by further compression of said portion of the tubulation to produce a base-metal-to-base-rnetal contact between the tubulation and the lead-wire by squeezing the tinned coats out of the basemetal-to-base-metal contact.

2. The method of sealing a tinned lead-wire of an impregnated capacitor to a casing closing end plug which comprises positioning the tinned lead-wire in a closefitting metal tubulation having a tinned central passage, crimping the tubulation into contact with the surface of said lead-wire over a limited area in a first step, melting the contacting tinned'coats at the crimped portion, squeezing said cr-irnped portion against said lead-wire in a second step to cause a displacing how of the tinned coats and to bring the base metal of the tubulation into contact with the base metal of the lead-wire.

References Cited in the file of this patent UNITED STATES PATENTS 1,991,767 McCullough Feb. 19, 1935 1,996,982 Sprague et al. Apr. 9, 1935 2,086,135 McIlvane July 6, 1937 2,211,659 Iohanson Aug. 13, 1940 2,739,277 Boisjol-ie Mar. 20, 1956 FOREIGN PATENTS 198,171 Austria Nov. 15, 1957 

1. THE METHOD OF SEALING AN ELECTRICAL COMPONENT CASING, SAID METHOD COMPRISING COMPRESSING A PORTION OF A CLOSE-FITTING TINNED TUBULATION OF AN END SEAL ONTO A TINNED LEAD-WIRE EXTENDING FROM AN ENCASED ELECTRICAL COMPONENT THROUGH THE TUBULATION, HEATING SAID TUBULATION AND SAID LEAD-WIRE AT THE COMPRESSED PORTION TO MELT THE TINNED COATS, DISPLACING SAID TINNED COATS BY FURTHER COMPRESSION OF SAID PORTION OF THE TUBULATION TO PRODUCE A BASE-METAL-TO-BASE-METAL CONTACT BETWEEN THE TUBULATION AND THE LEAD-WIRE BY SQUEEZING THE TINNED COATS OUT OF THE BASE-METAL-TO-BASE-METAL CONTACT. 